What is the future of causal models of cosmic structure formation?

Abstract

Recent research has severely constrained the standard ``defect'' models of cosmic structure formation. Here I discuss the nature of the problems with defect models, and place this discussion in the context of the big picture of cosmic structure formation. In particular, I classify models of cosmic structure formation as either ``causal'' or ``acausal'', and ask whether the problems with the defect models extend to all other causal models. I argue that determining the causal nature of the primordial perturbations is within the reach of modern cosmology, and that such a determination would yield deep insights into the very early Universe.

10 Pages including 4 postscipt figures. To appear in the proceedings of the "International Workshop on Particle Physics and the Early Universe" Ambleside, September 1997, L. Roszkowski Ed. (citations updated, typos corrected)